Prevention and treatment method for repair welding hot cracks of 800 DEG C-resistant nickel-based high-temperature alloy complex thin-wall structural member

Abstract

The invention relates to a method for preventing and treating repair welding hot cracks of a nickel-based high-temperature alloy complex thin-wall structural part resistant to 800 DEG C, belongs to the technical field of welding repair, and solves the problems that in the prior art, the nickel-based high-temperature alloy complex thin-wall structural part resistant to 800 DEG C is low in qualified rate and large in repair welding hot crack tendency, and welding spots are poor in high-temperature mechanical property after repair welding. The invention discloses a method for preventing and treating repair welding hot cracks of a nickel-based high-temperature alloy complex thin-wall structural part resistant to 800 DEG C. The method comprises the steps that a welding area is preheated to 300-600 DEG C before welding; the welding material is the same as the base material; the welding process is tungsten electrode argon shield welding, the welding current is less than or equal to 70A, and the diameter of a welding wire is less than or equal to 3mm. And the high-temperature strength of the structural part is ensured while the manufacturing qualification rate of the high-temperature alloy complex thin-wall structural part is improved.

Description

Technical Field

[0001] The invention relates to the technical field of welding repair, and in particular to a method for preventing and controlling hot cracks in repair welding of complex thin-walled structural parts of nickel-based high-temperature alloys resistant to 800°C. Background Art

[0002] High-temperature alloy structural parts, such as casings, pre-swirl nozzles, guide supports, etc., are key hot-end components of aircraft engines. Their performance directly affects the thrust, efficiency, durability and safety of the engine, and is one of the key factors in improving the overall performance of the engine. Due to the integrated and lightweight design requirements of the new generation of aircraft engines, current structural parts tend to adopt an integrated design. The castings are large in size, contain ultra-complex cavities and thin walls inside, and are prone to metallurgical defects during the casting process, which often require repair welding. However, since the new generation of aircraft engines requires the maximum service temperature of structural parts to exceed 800°C, in order to ensure the high-temperature strength of the structural parts, the alloys often contain high contents of elements such as Al, Ti, Nb, and Mo, and need to be repaired with bulk welding wire or alloy grade welding wire with high contents of elements such as Al, Ti, Nb, and Mo, which has a high tendency to weld hot cracks. At the same time, due to the complex structure of the castings and large thickness differences, stress concentration is easily generated during the welding process, exacerbating the generation of welding hot cracks.

[0003] Although there are many studies on the repair welding of nickel-based high-temperature alloys that can withstand 800℃, these studies all use dissimilar welding wires with good welding properties but poor mechanical properties for repair welding. Although the tendency of hot cracks in the welds is small, the high-temperature strength is low, which cannot meet the needs of the actual service environment. Summary of the invention

[0004] In view of the above analysis, an embodiment of the present invention aims to provide a method for preventing and controlling thermal cracks in repair welding of complex thin-walled structural parts of nickel-based high-temperature alloys resistant to 800°C, so as to solve at least one of the problems of low qualified rate of existing complex thin-walled structural parts of nickel-based high-temperature alloys resistant to 800°C, high tendency of thermal cracks in repair welding, and poor high-temperature mechanical properties of welds after repair welding.

[0005] The embodiment of the present invention provides a method for preventing and controlling hot cracks in the repair welding of complex thin-walled structural parts of nickel-based high-temperature alloys resistant to 800°C. Before welding, the welding area is preheated in two stages to 300-600°C; the welding material is the same as the parent material; the welding process is tungsten inert argon shielded welding, the welding current is ≤70A, and the welding wire diameter is ≤3mm.

[0006] Preferably, the welding process is performed in a vacuum welding chamber.

[0007] It is worth noting that the wall thickness of the welding area of ​​the thin-walled structural component is ≤3 mm and / or the welding area is located in the inner cavity of the structural component.

[0008] Furthermore, the two-stage preheating method of the welding area is:

[0009] S1. Preheat the entire structure at 150-250℃ for 10-40min, then immediately put it into the vacuum welding box to evacuate and fill it with argon;

[0010] S2. Locally preheat the welding area: preheat the solder joints to a temperature of 300-600°C.

[0011] Specifically, in S1, the vacuum welding box is first evacuated to <8Pa, and then filled with argon gas to -0.01MPa to +0.05MPa.

[0012] Preferably, in S1, the structural component is preheated in an oven or a heat treatment furnace; in S2, the solder joint is preheated by an induction heater or a heat drying gun.

[0013] Further, in S2, when a heat gun is used for preheating, the power of the heat gun is 1000W to 2000W, and double-sided preheating is performed on the welding area. The procedure of the double-sided preheating is as follows: after heating the front side for 30 to 90 seconds, the back side of the welding area is heated for 30 to 90 seconds, and the process is repeated 3 to 5 times, and finally the heating is terminated on the front side. When an induction heater is used for preheating, the induction coil is placed in the welding area, and the heating time is 30 to 120 seconds, wherein the power of the induction heater is 10kW to 20kW.

[0014] Preferably, the welding wire and tungsten electrode are pre-treated before welding, and the welding wire is repeatedly wiped with acetone or alcohol until there is no visible contaminant on the surface and it has a consistent metallic luster; the extreme end of the tungsten electrode is ground into a flat-bottomed cone, and the length of the tungsten electrode is 3cm-20cm.

[0015] It should be noted that the single repair welding time is less than 3 minutes; before each repair welding, the casting should be cooled to below 200°C.

[0016] Furthermore, when the welding area is a through hole, the repair welding sequence is first the periphery and then the center.

[0017] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0018] 1. The present invention adopts welding materials with the same material as the parent material, which can ensure the high-temperature strength of the structural parts, and reduce the temperature difference during welding by preheating before welding to reduce the thermal stress generated, thereby reducing the residual stress after welding and effectively reducing the tendency of thermal cracks; controlling the appropriate welding current and wire diameter, reducing the heat input, effectively reducing the generation of welding thermal cracks, and improving the qualified rate of high-temperature alloy castings.

[0019] 2. The present invention optimizes the preheating procedure before welding, adopts a two-stage preheating mechanism, and a dual preheating mechanism for the entire structural part and the welding area; the entire structural part is preheated before the local preheating of the welding area, which can effectively slow down the heat dissipation speed of the welding area and ensure the continuity of the temperature during the welding process. On the other hand, it can reduce the temperature gradient between the welding area and the main body of the structural part, further reducing the risk of stress concentration;

[0020] Strengthening the preheating of the welding area locally can effectively reduce the temperature difference between the arc and the base material during welding, thereby reducing the generated thermal stress, and then reducing the residual stress after welding, effectively reducing the tendency of thermal cracks;

[0021] By strictly controlling the overall preheating temperature of the structural parts, the preheating effect is ensured while reducing the impact on the working environment in the vacuum welding box.

[0022] 3. The present invention further optimizes the operation procedure and repair welding sequence, controls the single repair welding time, prevents local overheating and tungsten electrode melting loss from introducing high-density inclusions; adopts the repair welding sequence of first the periphery and then the center, effectively prevents stress concentration in the welding area, reduces the tendency of thermal cracks, and has a significant effect, especially for the repair welding of the perforated area where the heat input is more difficult to control during the welding process.

[0023] 4. The welding process and welding sequence of the present invention are highly versatile and can adapt to the welding requirements of 800°C resistant nickel-based high-temperature alloys in thin-walled areas, areas with uneven wall thickness, and complex inner cavity areas, avoiding the complexity of formulating different processes and procedures due to regional differences or changes in wall thickness, thereby significantly improving the efficiency of repair welding.

[0024] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0026] FIG. 1( a ) is a schematic diagram of the perforation welding sequence of a long seam according to the present invention;

[0027] FIG1( b ) is a schematic diagram of the welding sequence of a nearly circular through-hole according to the present invention;

[0028] Figure 2 This is a picture of the actual object after perforation welding in Example 1 of the present invention;

[0029] Figure 3 This is a real picture of the second embodiment of the present invention after perforation welding;

[0030] Figure 4 This is a real picture of the perforated welding of Example 3 of the present invention;

[0031] Figure 5 This is a picture of the actual object after perforation welding in Example 4 of the present invention;

[0032] Figure 6 This is a photo of the actual object after perforation welding in comparative example 1 of the present invention;

[0033] Figure 7 This is the X-ray image after perforation welding of Comparative Example 2 of the present invention;

[0034] Figure 8 This is a picture of the actual object after perforation welding in comparative example 3 of the present invention;

[0035] Fig. 9 Preheating pictures for the drying gun of the present invention;

[0036] Fig.10 This is a picture of the induction preheating of the present invention. DETAILED DESCRIPTION

[0037] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0038] Thermal cracks and strain aging cracks are prone to occur during the welding process of high-temperature alloys. Thermal cracks include solidification cracks, liquefaction cracks, etc. Compared with strain aging cracks, which are mainly prevented and controlled by post-weld heat treatment, the prevention and control of thermal cracks focuses more on metallurgical factors and the control of welding processes.

[0039] Nickel-based high-temperature alloys resistant to 800°C have a high tendency to hot cracks during welding due to the high content of elements such as Al, Ti, Nb, and Mo. In particular, the strengthening mechanism of precipitation-strengthened high-temperature alloys depends on the precipitation phase (such as γ' phase) formed in the alloy. Due to the influence of the welding thermal cycle, elements near the precipitation phase (such as Al and Ti) are prone to segregation. Based on the above reasons, if the parent material welding wire is used, the high Al and Ti content of the welding wire will cause the sensitivity to hot cracks to increase further. Therefore, in the prior art, when repairing nickel-based high-temperature alloys, heterogeneous welding wires with good welding performance and poor mechanical properties are generally used for repair welding. Although the tendency of hot cracks in the weld can be reduced, the high-temperature strength is low and cannot meet the needs of the actual service environment. With the increase in the requirements for the high-temperature strength of structural parts, the use of parent material welding wire is the best choice, and how to control the generation of hot cracks has become the key.

[0040] A specific embodiment of the present invention discloses a method for preventing and controlling thermal cracks in the repair welding of complex thin-walled structural parts of nickel-based high-temperature alloys resistant to 800°C. Before welding, the welding area is preheated in two stages to 300-600°C; the welding material is the same as the parent material; the welding process is tungsten inert argon shielded welding, the welding current is ≤70A, and the welding wire diameter is ≤3mm.

[0041] Specifically, the welding area is an area with a radius of 10-20 mm and a welding point as the center. The diameter of the welding wire is determined according to the welding current range.

[0042] Preheating the welding area before welding can reduce the temperature difference between the arc and the base material during welding, thereby reducing the thermal stress generated, and further reducing the residual stress after welding, effectively reducing the tendency of thermal cracks; controlling the appropriate welding current and wire diameter can reduce the heat input.

[0043] Preferably, the preheating temperature of the welding area before welding is 300° C., 350° C., 400° C., 450° C., 500° C., 530° C., 550° C., 600° C. The welding current is 50A, 55A, 60A, 65A, 70A.

[0044] Preferably, the welding process is carried out in a vacuum welding box, which effectively isolates the surrounding air, protects the welding area from oxidation, better controls the arc and molten pool, reduces welding defects, ensures sufficient argon protection and good weld accessibility.

[0045] Furthermore, the wall thickness of the welding area of ​​the thin-walled structural part is ≤3mm and / or the welding area is located in the inner cavity of the structural part. On the one hand, the structural part is large in size, contains ultra-complex cavities and thin walls inside, which easily produces metallurgical defects during the casting process and requires repair welding; on the other hand, the wall thickness and position of the welding area limit the release path of welding deformation, resulting in stress concentration in the welding area, which in turn generates welding stress and makes repair welding difficult.

[0046] It should be noted that the two-stage preheating method of the welding area is:

[0047] S1. Preheat the entire structure at 150-250℃ for 10-40min, then immediately put it into the vacuum welding box to evacuate and fill it with argon;

[0048] S2. Locally preheat the welding area: Preheat the welding area to a temperature of 300-600°C.

[0049] Preheating the welding area can reduce the temperature difference between the arc and the base material during welding. The higher the preheating temperature, the more conducive it is to reducing thermal stress. If the preheating temperature is too high, it will lead to excessive heat input in the welding area, which may cause overheating of the material or degradation of the performance of the heat-affected zone.

[0050] Before preheating the welding area locally, preheating the entire structure can effectively slow down the heat dissipation rate of the welding area. Too fast heat dissipation in the welding area will lead to insufficient pre-welding temperature of the welding area, affecting the temperature continuity during welding and increasing the risk of welding stress and cracks. On the other hand, it can reduce the temperature gradient between the welding area and the main body of the structure, further reducing the risk of stress concentration.

[0051] The overall preheating temperature of the structural parts needs to be strictly controlled. If the preheating temperature is too low, it cannot effectively slow down the heat dissipation speed. If the preheating temperature is too high, the working environment in the vacuum welding box will be harsh and the energy consumption will be too high.

[0052] Preferably, the overall preheating temperature of the structural parts in S1 is 150°C, 180°C, 200°C, 220°C, or 250°C.

[0053] Preferably, in S1, the vacuum welding box is first evacuated to <8Pa, and then filled with argon gas to -0.01MPa to +0.05MPa.

[0054] For example, in S1, the structural member is preheated in an oven or a heat treatment furnace; in S2, Fig. 9 , Fig.10 As shown, the welding area is preheated by an induction heater or a heat gun.

[0055] Specifically, in S2, when a heat gun is used for preheating, the power of the heat gun is 1000W to 2000W, and the welding area is preheated on both sides. The procedure of the double-sided preheating is: after heating the front side for 30 to 90 seconds, the back side of the welding area is heated for 30 to 90 seconds, and the heating is repeated 3 to 5 times, and finally the heating is terminated on the front side. Terminating the heating on the front side makes the temperature of the front side higher, which is conducive to controlling the temperature difference between the arc and the welding area in the front welding process to be smaller.

[0056] In S2, when the induction heater is used for preheating, the induction coil is placed in the welding area, and the heating time is 30 to 120 seconds, wherein the power of the induction heater is 10 kW to 20 kW.

[0057] Preferably, the welding wire and tungsten electrode are pre-treated before welding, and the welding wire is repeatedly wiped with acetone or alcohol until there is no visible contaminant on the surface and it has a consistent metallic luster; the extreme end of the tungsten electrode is ground into a flat-bottomed cone, and the length of the tungsten electrode is 3cm-20cm.

[0058] Specifically, the single repair welding time is less than 3 minutes; before each repair welding, the casting should be cooled to below 200°C to prevent local overheating and the introduction of high-density inclusions due to tungsten electrode melting.

[0059] Furthermore, the welding area is a through hole. When the welding area is a through hole, the welding time and number of times required are longer than those of the non-perforated area, and the heat input during the welding process is more difficult to control.

[0060] It should be noted that when welding the through-holes, the order of repair welding is first the periphery and then the center.

[0061] Exemplarily, as shown in FIG. 1( a ), when the through hole is in the shape of a long seam, the repair welding sequence is to perform repair welding from both ends of the through hole in the length direction to the middle.

[0062] Exemplarily, as shown in FIG. 1( b ), when the through hole is nearly circular, the repair welding sequence is to perform repair welding along the outer circumference of the through hole toward the center one circle at a time.

[0063] The order of repair welding from the periphery first to the center can prevent stress concentration at the perforated weld. Welding from the periphery first allows the weld to have space to shrink freely, reducing the concentration of heat input and thus reducing welding stress; otherwise, it will cause stress concentration because the welds of subsequent welds will be constrained by the first welded area, resulting in stress concentration and potential crack risk.

[0064] In summary, the present invention adopts welding materials with the same material as the parent material, which can ensure the high-temperature strength of the structural parts, and reduce the temperature difference during welding by preheating before welding to reduce the thermal stress generated, thereby reducing the residual stress after welding and effectively reducing the tendency of thermal cracks; controlling the appropriate welding current and wire diameter, reducing the heat input, effectively reducing the generation of welding thermal cracks, and improving the qualified rate of high-temperature alloy castings.

[0065] The method for preventing and controlling hot cracks in repair welding of complex thin-walled structural parts of nickel-based high-temperature alloys resistant to 800° C. according to the present invention is described below in conjunction with specific embodiments.

[0066] Example 1

[0067] This embodiment provides a method for preventing and controlling thermal cracks in repair welding of complex thin-walled structural parts of nickel-based high-temperature alloys resistant to 800°C.

[0068] The thin-walled structural part is the receiver made of K439B material.

[0069] The welding material is K439B body welding wire.

[0070] The pre-welding and repair welding process includes the following steps:

[0071] S1. Preheat the structural parts at 200℃ for 15min, then immediately put them into the vacuum welding box to evacuate and fill with argon;

[0072] S2. Use a 1500W heat gun to heat the front of the welding area for 60 seconds and then heat the back of the welding area for 60 seconds, alternating five times. The actual surface temperature of the front of the welding area is 340°C.

[0073] S3. Perform tungsten inert gas argon welding with a welding current of 60A and a wire diameter of Φ2mm. During welding, a single repair welding time is less than 3 minutes. Before each repair welding, wait until the casting cools down to below 200°C. The repair welding order for each welding point is the periphery first and then the center.

[0074] like Figure 2 As shown, the weld does not crack after welding, and there are no defects shown by fluorescence and X-ray. The high-temperature yield strength of the weld at 800°C reaches 770MPa, which exceeds 85% of the high-temperature yield strength of the base material at 800°C, meeting the service requirements.

[0075] Example 2

[0076] This embodiment provides a method for preventing and controlling thermal cracks in repair welding of complex thin-walled structural parts of nickel-based high-temperature alloys resistant to 800°C.

[0077] The thin-walled structural part is the receiver made of K439B.

[0078] The welding material is K439B body welding wire.

[0079] The pre-welding and repair welding process includes the following steps:

[0080] S1. Preheat the structural parts at 200℃ for 15min, then immediately put them into the vacuum welding box to evacuate and fill with argon;

[0081] S2. Use an induction heater with a power of 15 kW to heat the welding area for 90 seconds. The actual surface temperature of the welding area is about 530°C.

[0082] S3. Perform tungsten inert gas argon welding with a welding current of 60A and a wire diameter of Φ2mm. During welding, a single repair welding time is less than 3 minutes. Before each repair welding, wait until the casting cools down to below 200°C. The repair welding order for each welding point is the periphery first and then the center.

[0083] like Figure 3 As shown, the solder joint does not crack after welding, and no defects are shown in fluorescence and X-ray.

[0084] Example 3

[0085] This embodiment provides a method for preventing and controlling thermal cracks in repair welding of complex thin-walled structural parts of nickel-based high-temperature alloys resistant to 800°C.

[0086] The thin-walled structural part is the receiver made of K439B.

[0087] The welding material is K439B body welding wire.

[0088] The pre-welding and repair welding process includes the following steps:

[0089] S1. Preheat the structural parts at 150℃ for 35min, then immediately put them into the vacuum welding box to evacuate and fill with argon;

[0090] S2. Use an induction heater with a power of 15 kW to heat the welding area for 50 seconds. The actual surface temperature of the welding area is about 350°C.

[0091] S3. Perform argon tungsten electrode welding with a welding current of 65A and a wire diameter of Φ3mm. During welding, a single repair welding time is less than 3 minutes. Before each repair welding, wait until the casting cools down to below 200°C. The repair welding order for each welding point is the periphery first and then the center.

[0092] like Figure 4 As shown, the solder joint does not crack after welding, and no defects are shown in fluorescence and X-ray.

[0093] Example 4

[0094] This embodiment provides a method for preventing and controlling thermal cracks in repair welding of complex thin-walled structural parts of nickel-based high-temperature alloys resistant to 800°C.

[0095] The thin-walled structural part is the receiver made of K439B material.

[0096] The welding material is K439B body welding wire.

[0097] The pre-welding and repair welding process includes the following steps:

[0098] S1. Preheat the structural parts at 250℃ for 15min, then immediately put them into the vacuum welding box to evacuate and fill with argon;

[0099] S2. Use an induction heater with a power of 15 kW to heat the welding area for 60 seconds. The actual surface temperature of the welding area is about 400°C.

[0100] S3. Perform tungsten inert gas argon welding with a welding current of 60A and a wire diameter of Φ2mm. During welding, a single repair welding time is less than 3 minutes. Before each repair welding, wait until the casting cools down to below 200°C. The repair welding order for each welding point is the periphery first and then the center.

[0101] like Figure 5 As shown, the solder joint does not crack after welding, and no defects are shown in fluorescence and X-ray.

[0102] Comparative Example 1

[0103] This embodiment provides a method for preventing and controlling thermal cracks in repair welding of complex thin-walled structural parts of nickel-based high-temperature alloys resistant to 800°C.

[0104] The material of the structural parts and the welding material are the same as those in Example 1, and the preheating before welding and the welding process are basically the same as those in Example 1, except that the welding current is larger, which is 100A.

[0105] like Figure 6 As shown, the solder joint cracked after welding and the repair welding failed.

[0106] Comparative Example 2

[0107] This embodiment provides a method for preventing and controlling thermal cracks in repair welding of complex thin-walled structural parts of nickel-based high-temperature alloys resistant to 800°C.

[0108] The material of the structural parts and the welding material are the same as those in Example 1, and the preheating before welding and the welding process are basically the same as those in Example 1, except that the single repair welding time exceeds 6 minutes.

[0109] like Figure 7 As shown in the figure, the X-ray after welding shows that there are cracks in the weld and it contains high-density inclusions, and the repair welding fails.

[0110] Comparative Example 3

[0111] This embodiment provides a method for preventing and controlling thermal cracks in repair welding of complex thin-walled structural parts of nickel-based high-temperature alloys resistant to 800°C.

[0112] The material of the structural parts and the welding material are the same as those in Example 1, and the preheating and welding process are basically the same as those in Example 1, except that the repair welding sequence of each welding point is not performed according to the principle of first the periphery and then the center.

[0113] like Figure 8 As shown, the solder joint cracked after welding and the repair welding failed.

[0114] Comparative Example 4

[0115] This embodiment provides a method for preventing and controlling thermal cracks in repair welding of complex thin-walled structural parts of nickel-based high-temperature alloys resistant to 800°C.

[0116] The thin-walled structural part is the receiver made of K439B material.

[0117] The welding material is IN625 welding wire.

[0118] The pre-welding treatment and repair welding process steps are the same as those in Example 1.

[0119] The 800°C high temperature yield strength at the weld point is only about 420 MPa, which is difficult to meet the service requirements at 800°C. However, the 800°C high temperature yield strength at the weld point of Example 1 reaches 770 MPa, which exceeds 85% of the 800°C high temperature yield strength of the main body material and meets the service requirements.

[0120] Comparative Example 5

[0121] This embodiment provides a method for preventing and controlling thermal cracks in repair welding of complex thin-walled structural parts of nickel-based high-temperature alloys resistant to 800°C.

[0122] The material of the structural parts and the welding material are the same as those in Example 1, and the preheating and welding process are basically the same as those in Example 1, except that the preheating temperature at the welding point is 200°C.

[0123] The solder joint cracked after welding and the repair welding failed.

[0124] Comparative Example 6

[0125] This embodiment provides a method for preventing and controlling thermal cracks in repair welding of complex thin-walled structural parts of nickel-based high-temperature alloys resistant to 800°C.

[0126] The material of the structural parts and the welding material are the same as those in Example 1, and the preheating before welding and the welding process are basically the same as those in Example 1, except that the overall preheating temperature of the structural parts is 120°C.

[0127] The solder joint cracked after welding and the repair welding failed.

[0128] Comparative Example 7

[0129] This embodiment provides a method for preventing and controlling thermal cracks in repair welding of complex thin-walled structural parts of nickel-based high-temperature alloys resistant to 800°C.

[0130] The material of the structural parts and the welding material are the same as those in Example 1. The preheating before welding and the welding process are basically the same as those in Example 1. The difference is that the diameter of the welding wire selected during welding is 4 mm.

[0131] In the range of welding current ≤70A, the welding wire cannot be completely melted due to the large diameter of the welding wire, that is, the welding wire cannot be fully melted to complete the welding of the weld spot.

[0132] In Example 1 and Example 2, the body welding wire is used to repair the perforation of the thin-walled structural parts by welding, and the two preheating temperatures and the welding process conditions and sequence are strictly controlled to ensure that the weld does not crack after welding, and the fluorescence and X-rays show no defects, and the 800°C high temperature yield strength at the weld meets the service requirements. It can be seen from Comparative Example 1 and Example 1 that the welding current exceeds the design range of the present invention during welding, resulting in cracking of the weld and failure of the welding repair; it can be seen from Comparative Example 2 and Example 1 that the single welding time during welding is too long, resulting in increased heat input, cracking of the weld, and failure of the welding repair; it can be seen from Comparative Example 3, Comparative Example 5, Comparative Example 6 and Example 1 that the welding sequence and preheating conditions do not meet the requirements of the present invention, all resulting in cracking of the weld and failure of the welding repair; it can be seen from Comparative Example 4 and Example 1 that the welding material is different from the parent material, although the crack risk can be reduced, but the 800°C high temperature yield strength at the weld is difficult to meet the service requirements; the diameter of the welding wire in Comparative Example 7 is too large, and the welding repair operation cannot be completed under the welding current within the design range of the present invention.

[0133] In summary, the present invention adopts welding materials with the same material as the parent material, which can ensure the high-temperature strength of the structural parts, and reduce the temperature difference during welding by preheating before welding to reduce the thermal stress generated, thereby reducing the residual stress after welding and effectively reducing the tendency of thermal cracks; controlling the appropriate welding current and wire diameter, reducing the heat input, effectively reducing the generation of welding thermal cracks, and improving the qualified rate of high-temperature alloy castings.

[0134] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preventing and controlling hot cracks in repair welding of complex thin-walled structural parts of nickel-based high-temperature alloys resistant to 800°C, characterized in that: Before welding, the welding area is preheated in two stages to 300-600°C; the welding material is the same as the parent material; the welding process is tungsten inert argon shielded welding, the welding current is ≤70A, and the welding wire diameter is ≤3mm.

2. The control method according to claim 1, characterized in that: The welding process is carried out in a vacuum welding box.

3. The control method according to claim 1, characterized in that: The wall thickness of the welding area of ​​the thin-walled structural component is ≤3 mm and / or the welding area is located in the inner cavity of the structural component.

4. The control method according to claim 1, characterized in that: The two-stage preheating method of the welding area is: S1. Preheat the entire structure at 150-250℃ for 10-40min, then immediately put it into the vacuum welding box to evacuate and fill it with argon; S2. Locally preheat the welding area: Preheat the welding area to a temperature of 300-600°C.

5. The control method according to claim 4, characterized in that: In S1, the vacuum welding box is first evacuated to <8Pa, and then filled with argon gas to -0.01MPa to +0.05MPa.

6. The control method according to claim 4, characterized in that: In S1, the structural parts are preheated in an oven or a heat treatment furnace; in S2, the welding area is preheated by an induction heater or a heat drying gun.

7. The control method according to claim 4, characterized in that: In S2, when a heat gun is used for preheating, the power of the heat gun is 1000W~2000W, and double-sided preheating is performed on the welding area. The procedure of double-sided preheating is: after heating the front side for 30~90s, the back side of the welding area is heated for 30~90s, and the process is repeated 3~5 times, and finally the heating is ended on the front side. When an induction heater is used for preheating, the induction coil is placed in the welding area, and the heating time is 30~120s, wherein the power of the induction heater is 10kW~20kW.

8. The control method according to claim 2, characterized in that: Before welding, the welding wire and tungsten electrode are treated before welding. The welding wire is repeatedly wiped with acetone or alcohol until there is no visible contaminant on the surface and it has a consistent metallic luster; the end of the tungsten electrode is ground into a flat-bottomed cone with a tungsten electrode length of 3cm-20cm.

9. The control method according to claim 1, characterized in that: The single repair welding time is less than 3 minutes; before each repair welding, wait until the casting cools down to below 200℃.

10. The control method according to claim 1, characterized in that: When the welding area is a through hole, the repair welding sequence is first the periphery and then the center.

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